Pharmacodynamics PDF

Pharmacodynam ics  Targets of drugs Receptors Enzymes Ion channels Carrier molecules Physical or Chemical  Drug receptors Highly specific, highly sensitive binding site Found on the surface of the cell membrane, enzyme molecules on nuclear membranes...

Pharmacodynam ics  Targets of drugs Receptors Enzymes Ion channels Carrier molecules Physical or Chemical  Drug receptors Highly specific, highly sensitive binding site Found on the surface of the cell membrane, enzyme molecules on nuclear membranes.  Receptor Specificity – There are a number of specific ligands and a number of associate receptors Affinity The extent to which the ligand is capable of binding and remains bound to a receptor High affinity: The ligand bind well and remains bound for long enough to activate the receptor Low Affinity: The ligand binds less well and may not remain bound long enough to activate the receptor  The receptor intrinsic activity The extent to which the ligand activates the receptor High intrinsic activity: the ligand produces a large effect on the post synaptic cell Low intrinsic activity: the ligand produces a small or inconsistent effect on the post synaptic cell  Classes of Ligands Agonists – High affinity – High intrinsic activity Antagonist – High affinity – Low intrinsic activity  Agonists An agonist is a drug that binds to a receptor and activates it to give a response There are 2 types of agonists: 1. Full agonist: is a drug when bound to a receptor produces 100% of the maximum possible biologic response 2. Partial agonist: a drug that produce less than 100% of the maximum possible biologic response no matter how high their concentration  Antagonist An antagonist is a drug that bind to a receptor and produce no response. Type of drug antagonism: 1. Receptor antagonists a) Competitive: the antagonists competes with the agonist at the same receptor site of an agonist and binds to it reversibly. By increasing the concentration of drug agonist the antagonism is abolished. E.g. antihistamine competes with histamine at its receptor site b) Non competitive: the antagonist binds irreversibly to a different site on the enzyme e.g. than the agonist, noncompetitive agonists can not overcome by increasing the concentration of the drug agonist. E.g. succinylcholine is irreversible neuromuscular blocker.  Continue … 2. Physiological antagonism: e.g. glucagon and insulin. Histamine and epinephrine 3. Chemical antagonist: is the type of a drug that acts by binding chemically to the compounds and inactivates it. E.g. chelating agents, charcoal (poisoning with iron) 4. Pharmacokinetic antagonist: by increasing the metabolism and excretion of a drug, e.g. enzyme induction to speed metabolism